Research has shown that low levels of vitamin A during a cow's pregnancy are associated with abortions, stillbirths, and weak-born calves. In addition to playing an important role in reproductive efficiency, vitamin A is essential for vision, bone growth, and maintaining epithelial tissue such as skin and hooves in cattle.
Animals obtain vitamin A from consuming green forage and/or the addition of supplements to their diet. Lush green pastures contain high amounts of vitamin A but as plants mature and during times of drought, the amount of the essential vitamin decreases.
In general, animals obtain adequate amounts of vitamin A by grazing green forage. Animals grazing on green pastures will build a healthy store of vitamin A in the liver. When vitamin A is in short supply, the store in the liver prevent deficiencies. According to Oklahoma State University Extension Beef Cattle Specialist Dr David Lalman the stores should last two to four months during times of deficiency.